notes to teachers this slide should not be displayed

Notes to teachersThis slide should NOT be

displayedThe purpose of this presentation is to…

•Introduce the basic science behind the “Goo” experiment / investigation.

•There is an opportunity to emphasise that there are a number of representations used to explain what happens in nature. These are NOT actually what happens, but that they are “Models” to help us visualise a specific set of circumstances.

•The presentation is NOT intended to teach topics for the first time, but to revise some aspects of chemistry (monomer / polymer / covalent bonding) and to give an insight into an aspect of chemistry at A’ level (polarity, H bonding).

•Taken with the experiment, there is an opportunity here to highlight the fact that chemistry and physics can be linked together to modify the mechanical properties of a polymer by using a reaction to cross link polymer chains and design a polymer with a specific viscosity. An investigation of viscosity v cross links could follow. This using science for practical (and commercial) use is Materials Science.

Goo – How it works

(Without getting too stuck on details)

Martin Carr(Oxford University Department of

Materials)

email: Martin.Carr@materials.ox.ac.ukweb: http://outreach.materials.ox.ac.uk

Easy Words

Goo is made from a polymer called…

Poly Vinyl Alcohol

…which is the main part of PVA glue

Poly = Lots of identical bits

Vinyl = Name for repeat units of C-C

Alcohol = A special, covalent –OH group

Easy Molecules

This is how we represent Vinyl alcohol…

C C O

C C

O

C C OH

C COH

C2H5OH

C2H3OH

This is how we represent ordinary alcohol…

Easy Polymer

C C

OH

n

Hundreds of thousands of Vinyl Alcohol monomer molecules (mer means molecule) join together in a chemical reaction to make a Polymer.

The molecule is too big to draw every single atom, so we have a shorthand where “n” is the number of joined monomer molecules…

Medium – Bonding

O H

• The electrons are NOT always equally shared

• Polymers are made using covalent bonds to join atoms.

• Electrons are shared between atoms.• The Alcohol, -OH, also uses covalent bonds.

Slightly-ve

Slightly+ve

Slightly-ve O H

Representing a Polar molecule

Harder – Hydrogen Bonding

C C

OH

C C

OH

C C

OH

C C

OH

C C

OH

C C

OH

…are next to similar molecules…The groups attract and make it harder to

slide past each other.

Long Molecules with lots of Polar, -OH, Groups

Electrostatic Attraction(Hydrogen Bond)

The Finale

Borax -- ion

C C

OH

C C

OH

C C

OH

CC

OHC

C

OH

CC

OH

CC

O

H

CC

O

H

CC

O

H

The Borax 2- anionAttracts more stronglyAnd holds moreChains together

Thank You For

Listening.

Now it’s your turn…